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ON the PARASPHENOID of the BRACHYTHORACI the First

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ON the PARASPHENOID of the BRACHYTHORACI the First A eTA PALA EO;\,TOLOGICA POLONICA vet. I 1 956 No . 2 JULIAN KULCZYCKI ON THE PARASPHENOID OF THE BRACHYTHORACI A bst ract . - A description is given of the Brachythoraci parasphenoid as compared w ith th e corresponding structure dm Ao ant~idiiJalIl!S and some Crossopterygnans (Po­ rolsp idae jvand ',viloh dhe Acanthodierr -anter-ior-basai. INTRODUCTION The fi rst desc rip tion 0.£ the parasphenoid 0.£ the Arthrodires was made by E. S. Hills (1936) upon discovering inthe endocranial floor of 1Jhe Coc­ costeus (= Buchanosteus) osseus the presenceof 'a "thiokened part com­ pos ed orf solid bone' with a som ewhat complicated structure. A dermal element, coating the very same region of eIIldlOcT'ani~m of I Kujdanovia spis buczacziensis but showing a much simpler structure, was des cr ib ed by E. A. Stensio (1942). In an. addendum to his next paper on the cramum and cervical jodnt of cth e Dolichothoraci (Acanthaspida) (1945), Stensio is 10010 'the conclu­ sion thetthe dermal element, decribed by him and by Hidlsvconstdtutes the p arasphen oid. In the same paper Stensio writes thaJt in certain Bra­ chythoracid Arthrodires from Wildungen (Erromenosteus, Trematosteus, Brachyosteus) he had ascer-tained ,the presence of the parasphenodd, sha­ ped as .a powerful bone, extendin g, as it does in the Crossopteryglans and most of the Paiaeonisciformes, backwards to underneath the tran­ sition al part between the orbito-temporal and the otic regions of the endocr anium.E. A. Stensio believes fu:at th~s element' is provided with a paired processus ascendens, In their paper on the anterior superogn athal of Gorgonichthys, D. H. Dunkle and P. A. Bungart (1946) published a dJr.aiWdalg representing the parasphenoid of Dinichthy3 terreUi amd Heintzichthys gouldii mentio­ ning in the text fhat the SUiPeI':ognartlha:l elements are iJnJtimaJtely associa­ ted with a parasphenoid-ljke plate which is apparently to be homologised with the arsterior-basal element of the Acanthodians. The most recent reference to this element, here under consideration, is to be found iJn a paper by E. Jarvik (1954). When speaking of his hypothesis concerning the developmenr of parasphenoid in fishes, that 104 J UI.IAN KULCZYCKI author expr esses an opinion that in the Arthrodires the home, as m en­ tion ed above, r ep resents a primitive typ e of structure, apparently w ith out ascending p rocesses. Basing h is state men t on an unpublished paper by StOOo9i6 h e also alleges that th e developmen t of the p arasphenoid in Arthrodires is characterised b y disintegrati on 'an d r educ tion. Kujdanoviaspis buczacziensis and Buchanosteus osseus are the only r epresentatives of 'the Anthrodires w hose parasphenoids have been re­ ported upon at any lengrth. Since, as sh own by Stensio, both, th e latter of t hese forms, as well as Kujdanoviaspis, belong to. the Arctolep id a, no de tasled d escription of the par asphenoid of Brachy thorac i is thus far available. There a re three sp ecimen s of these bones in the fossil m ater ial dep o­ sited at the Muzeum Ziemi (Museum of the Ear th) in Wa rszawa a nd collected by l ate Mrs. Z. Gorizdro-Kulczycka in ,'fue Upper Devonian of Kieke. Two of them w ere discovered in association with other skull fragments belonging to DinichthYJ d . pu stulosus , and to 'the represen ­ tative of a new genus of Brachythoraci, probably closely r elated to Pholidosteus. A descr ip tion of these fragments will be given, in a forth­ coming paper. No fossil r em ains were found associat ed w ith the th ird specimen. Land d: ts generic and family appur tenance, cannot, therefore, be established. Never-theless its close resemblance to the parasphenoid of Dinich thys terrelli and Heintzichthys gouldii as fi­ gur ed in the drawing by Dunkle and Bun gart , testifies to its refe­ l'ab ility to the Brachyithorac i. This specim en is in the m ost complete state of pr eservation of the three at the writer's disposal. T hrough treat­ ment in acetic acid som e of its very d elicate structur al details h ave been disclosed and it is on this specimen that the writer has based h is p r esent description of the parasphenoid of Br achy thoraci. The writer's thanks are due to Professor D .W. Obrutseh ew of Moscaw a nd to Dr. D. H. Denison of Chicago for the valuable h ints received. from them by way of correspondance wh ile he was workin g on h is description of Devoniari fishes fromthe Holy Cross Mts. He is also p articularly m­ debted to Professor W. Gross of the Berlin Humbold t University for makirng accessible to him the collection of fosssl fishes <lit the university's palaeontclogicad institute, and for ,tJhe fniendly advice extended to the writer during h is brief visit a t fh e laboratory oper ated under the ma­ nagemen t of Prof. Gross. DESCRIP T IO N The parasphenoid of the Brachyfhoraci displays a r ather complicated structure. Two parts may be differentiated in t his h one, n amely the anterior (pa) tin the form of a s trong plate w ith a sub-cordate outline, ox H IE PARASP HDIOID OF THE BRACHYTHORA CI 105 terminating in a sharp apex projected anteraoriy, and the posterior (pp.) tran sversally elongated , thick around the midpoirit and thin around the edges . Tr an sversally the an t erior cor dat e p ar t (pa.) .is somewhat concave on the ventral side, and convex dorsally . At the sa m e tim e its lateral edges rather mm up in the dorsal direction, p anticular'ly so in rts broad poste­ rior region . Longitud in ally t he ante rior cordate p art bends gradually dorsad as it approaches itsantenior limit. On the ventral side, along the mid -line, a longitudinal crest (cr. m.) occurs in some forms (though ab­ sent in the specim en incertae fam iliae, showing the best state of preser­ vation ), more or less sharply edged , w ith h eight in cr easing anterior ly. Its basal wid th increases in the same direction. The crest is par ticular.l y d istinct in the parasphenoid of Dinichthys cf. pustulosus where it r eaches tcfhe anterior end of the elemerrt iand rt er rninates 'in a sharpened pro­ cess. In t his form the longutud in al crest p asses posteriorl y into a rather small fl at area (a. tub.) spotted b y minute tubercles identical to those found on the external surface of t he dermal bones of the skull. A longi­ tu dinal groove r uns dorsally along the mid-line of the anterior cordat e par t of the paeasphenoid (sm.). The free bone edge is grooved and ser­ rated. The pos terior p art (pp .) is unfortunately in 'a state of incomplete pre­ se rvati on. The lacking d etails are the more delicate marginal parts, in the form of thin lat eral lamellar processes (prl. v .), situated ventrally, w hose ou tl in e h as b een figured b y Dunkle and Bungart (1946) In their drawing of t he parasphenoid of Dinich th ys terr eHiand Heintzichthy s gouldii. On the base of the cited drawing it may be :iJnf,eu-r ed, that these processes are very well d evelop ed in Dinichthys terrelli, w hile irn Hein­ t Z i c h t~ys gouldii they ar e rather rudim entary. The p osterior part of the parasp henoid of Br achythor aci tran sversally somewh at con cave, prese nts a perfectly smooth and even ventral surface, Jack ing an y d etails. It is separ ated from the anterior corda te part by a di­ stin ct transverse groove (s. tr.) wh ose course across 'fu e element is tr aced at an angl e with anteriorly p oint ed ap ex . Medially the gr oove is parti­ tion ed by a bon e lamella pierced by a large foramen communicating w ith the left and right portions of the groove. 'Dhis gives the semblance of a delicate bone-bridge spanning the oern!uml region of the groove (p .). The ven t ral side olf iJhe bridge p aJSiS€ S wirth mo signs of demarcation to the ven tral surface of the anterior corda te part, while from the posterior part ,it is se parated by a narrow groove ccmmun icating a t both ends with the tr ansverse groove w hich transacts the whole element. Close to the bone m argin a minor groove branch es off on both sides into the drans­ ve rse groove (pl, II, fig. 7) and traverses the lateral surface running 00- 106 J ULI AN KULCZYCKI teriorly to the dorsal side of thearsteriorcordate pa.rt of the element, where it soon disa pp ears. In the mid-part of the groove, on both sides of the m edian bridge, there are two sym metrically arranged, faiTl y large foramina (c. aci.) separat ed by a bone lamella (pl. I, fig. F ; pl. II . fig. 6), vertically piercing 1Jhe parasphenoidand communicating w ilith a ba­ sin-like depression situated centraily on the d or sal side of th e elem ent. A r ather small ridge (cr. fh.) is found betw een the two foramin a of the depression, w ith its one end coalescing imp ercep tib ly w ith the front wall of 'the depression, wh ile the other end terminates as 'a fnee process on the back wall.
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